Simultaneous preparation of carbonyl sulfide and ammonium thiocyanate

ABSTRACT

A process for the simultaneous preparation of carbonyl sulfide and ammonium thiocyanate, which comprises heating and reacting urea with carbon disulfide at liquid phase, in aliphatic monohydric alcohol of one to four carbon atoms serving as the reaction medium.

United States Patent Nakamura et al.

[4 1 Mar. 28, 1972 [54] SIMULTANEOUS PREPARATION OF CARBONYL SULFIDE AND AMMONIUM THIOCYANATE [72] Inventors: Shizuo Nakamura, Tokyo; Masanobu Ito,

Sagamihara, both of Japan Sagami Chemical Research Center, Tokyo, Japan [22] Filed: Sept. 29, 1970 [211 App]. No.: 76,640

[73] Assignee:

[52] US. Cl. [51] Int. Cl. ...C0lc 3/20, COlb 31/26 [58] Field of Search ..23/75, 134, 203 R [56] References Cited OTHER PUBLICATIONS Landenburg: Berichte, Vol. 1, 1868), pp. 273- 274 Primary Examiner-Oscar R. Vertiz Assistant Examiner--Hoke S. Miller Attorney-Wenderoth, Lind & Ponack [57] ABSTRACT 6 Claims, No Drawings SIMULTANEOUS PREPARATION OF CARBONYL SULFIDE AND AMMONIUM THIOCYANATE This invention relates to a process for the simultaneous preparation of carbonyl sulfide and ammonium thiocyanate. More particularly, the invention relates to a process for the simultaneous preparation of carbonyl sulfide and ammonium thiocyanate, by heating and reacting urea and carbon disulfide at liquid phase, in lower alcohol serving as the reaction medi- Carbonyl sulfide has been collecting attention as a valuable starting material for making active ingredient of agricultural chemicals, particularly herbicides, and its economical production on industrial scale has been the demand of the trade. Ammonium thiocyanate also is a valuable substance, well known as the additives of synthetic resin, stabilizer of hydrogen peroxide, photographic chemicals, fertilizers, herbicides, and the starting material to prepare thiourea.

The main reaction intended in the invention can be expressed by the formula below:

Concerning the reaction between urea and carbon disulfide, studies of A. Ladenburg Ber., l,273(l868) is known of old.

He reported that, when the named two substances were together heated in a sealed tube at 110C. for several hours, formation of carbonyl sulfide was observed. However, his report is entirely silent on the yield. Ladenburg also surmised the reaction mechanism to be corresponding to the reaction formula (1) given above, but as to the ammonium thiocyanate he only wrote the chemical formula of CSNH-NH, in the reaction formula, never elaborating on its identification or quantitative relation.

According to our reproductive experiments, no reaction takes place under 2 hours heating at 1 C., as demonstrated also in the later given Control. We observed the state of the system in sealed glass tube in the above experiment, and confirmed that the urea crystals were present in the liquid carbon disulfide undissolved, showing no color change. The urea was molten to form liquid phase at 140 C., but the reaction rate was extremely low. At 150 C., only in the presence of excessive carbon disulfide, appreciable progress of the reaction was observed, and the liquid was colored yellow. However, the quantity of carbonyl sulfide in the formed gas was only minor, and considerable quantity of carbon dioxide was present as mixed therewith.

No report on the above reaction is available after the above Ladenburgs study, and the reaction has never received industrial concern.

It has now been found that when urea and carbon disulfide are heated and reacted in anhydrous, aliphatic lower monohydric alcohol serving as the reaction medium, carbonyl sulfide is formed at a high reaction rate, with the yield as high as approximately 95%, and that simultaneously therewith, ammonium thiocyanate is formed at similarly high yield.

Accordingly, the main object of the invention is to provide a process for making carbonyl sulfide and ammonium thiocyanate from urea and carbon disulfide with industrial advantage.

The fact that the reaction of formula (I) is effectively promoted in the presence of lower alcohol is indeed surprising, when the following circumstances are considered.

First of all, it is anticipated that the two reactants could not produce the object compounds at high yield, because the alcohol itself would react with these reactants. It is well known that alcohol reacts with carbon disulfide, particularly in the presence of minor amount of alkali, to produce the corresponding mercaptan, and also that alcohol reacts with urea to produce alkyl carbamate and biuret (Refer, for example, to U.S. Pat. No. 2,871,259). In view of such known facts, it is only logical to expect that the presence of alcohol will rather interfere with the main reaction intended by the subject invention. Therefore, it is entirely unpredictable that the reaction of formula (I) predominantly takes place as in the subject invention. We discovered this fact which is quite contrary to the seemingly logical presumption. This is probably because the concurrent presence of the two starting materials, urea and carbon disulfide, and the formed ammonium thiocyanate inhibit the above-described undesirable reactions of each reactant with alcohol.

Secondly, when organic solvents other than the lower alcohols are used as the reaction media, for example, acetone or dimethylsulfoxide, in the similar reaction, decomposition takes place to cause coloring 'and precipitation of side product. Also if ethers such as ethyl ether, dioxane, or polyhydric alcohols such as glycol, glycerol, etc. are used, the reaction is not effectively accelerated, and in all cases the recovery of object products at high yields are never achieved. Therefore, the newly discovered fact, that the lower alcohols only do effectively promote the reaction of formula (I), is entirely unpredictable. Thus, the advantageous result achieved by the presence of lower alcohols is not only that caused by homogenization of the reaction system by the solvent, but also presumably that caused by the activity characteristic to such alcohols only.

Hereinafter the invention will be more fully explained.

The subject process for the simultaneous preparation of carbonyl sulfide and ammonium thiocyanate comprises heating and reacting urea with carbon disulfide at liquid phase, in an aliphatic, monohydric alcohol of one to four carbon atoms serving as the reaction medium.

The lower alcohols useful as the reaction medium include methanol, ethanol, propanol and butanol. Among the named alcohols, methanol exhibits high solubility of urea, one of the starting materials, and consequently use of only minor amount thereof is sufficient for the purpose, allowing to maintain high concentration of the starting materials in the reaction system. As the result, the rate of the main reaction can be increased, and the side reaction between urea and alcohol can be inhibited to the minimum. Furthermore, methanol has also high solubility of the formed ammonium thiocyanate, facilitating the operations. Thus methanol is the most preferred reaction medium. Whereas, ethanol has been dissolving ability of urea compared with methanol, but has the advantage of higher solubility of carbon disulfide.

It is desirable that the quantity of lower alcohol should be at least sufficient to maintain the reaction system at homogeneous phase at the reaction temperaturelf it is less, the reaction system tends to become heterogeneous, and the reaction rate is reduced. Whereas, if it is excessively great, the reaction rate is reduced and side reactions are increased. The optinum quantity of the lower alcohol can easily be determined by simple preliminary test, according to the type of thealcohol and reaction temperature employed. Generally speaking, the quantity is within the range of approximately equal to twice the total sum of the starting materials. Use of greater quantity is not impossible, but it is recommended that the alcohol should never exceed approximately seven times the sum quantity of the starting materials. It should be put into consideration that, the alcohol of a quantity insufficient to keep the reaction system at homogeneous phase at room temperature might form homogeneous phase upon temperature rise to the level suitable for the reaction.

The reaction temperature is suitably selected within the range of -190 C., preferably l20-160 C. Under such temperatures, the reaction is performed in an air-tightly closed vessel, under autogenous pressure. At low reaction temperatures, obviously the reaction rate is low. Whereas, high temperatures exceeding 190 C. are also disadvantageous, because side reactions are increased and the autogenous pressure becomes objectionably great. The autogenous pressure reaches in most cases 30- 70 kg./cm. when methanol is used at the reaction temperatures ranging from to l60 C. The reaction time may range from 10 minutes to 5 hours. The reaction rate is generally high, with minor difference depending on the temperature. At l60-l 20 C., the maximum yield of the object product is reached within approximately 20 minutes to 5 hours, but the yield of ammonium thiocyanate is somewhat reduced as the reaction progresses, since the product is partially isomerized to thiourea, or cause secondary reaction with carbon disulfide.

Under the conditions given in the later-appearing Examples,

Hereinafter the invention will be further explained with reference to Examples and Controls. The product gas was analyzed by means of gas chromatoragphy and volumetric analysis by titration of gas-absorbent liquid.

dustrial scale production, concerning the starting materials. That is, from economical reasons, carbon monoxide-generating apparatus must be of considerably large scale. Consequently, the carbonyl sulfide production must also be practiced on large scale to secure any profit. lf carbon monoxide supply is sought from outer source, the expenses necessary for its handling, transfer, storage, etc. will incur innegligible influence on the cost price of the product, because carbon monoxide is a permanent gas. In contrast thereto, the process and equipments of the invention are very simple, and carbonyl in most cases the secondary change of ammonium thiocyanate 5 Concerning the liquid phase, ammonium thiocyanate was takes place. In order toobtain ammonium thiocyanate at identified by infrared spectrum and quantitatively it was yields higher than those achieved in the Examples, the reacanalyzed by silver nitrate titration, and as for urea, the amtion time may be shortened. Under suitably selected condimonia generated by the decomposition of it with ureas was tions, yields higher than 90% can easily be accomplished. measured to estimate its quantity.

The quantitative ratios of the two starting materials are not e g of ur d 20 gf carbon disulfide were critical. Normally the ratio of 1:1 (molar ratio) in accordance .charged in a pre s m glass Vessel Wlthm" Radio" medium. with the formula (I) and those in the vicinity of equimolar and heated to Various mp r 35 -r -s and point, i.c., 111.2 to 1.2:] in molar ratio are applied with 150 C. h stirring- F m pr d cts were analyzed with preference. Ratios outside the specified range are not imperthe results as S Table missible, but those outside the range of l:4 to 4:1 in moi ratio should be avoided. Normally when greater quantity of carbon- Yield of yl sulfide is wanted, excessive quantity of carbon disulfide is 12;"? :2?" 3:? used, and if greater yield of ammonium thiocyanate is desired, urea is used in excess.

. 1 o l o 5 I'd a o The gaseous phase of the reaction product contains the I 2 z formed carbonyl sulfide as the chief component, as well as 140 85 Two liquid 0.06 vapors of unreacted carbon disulfide and the alcohol em- P f ployed as the medium, with very minor quantities of sidez i 'i produced hydrogen sulfide, carbon dioxide, etc. The liquid phase comprises the formed ammonium thiocyanate as disqh d th n db F m solved in the alcohol used as the medium. Each of the ob ect e of locyanm'on was y a product can be isolated through suitable separation and purifi- EXAMPLE 1 cation as desired.

As so far explained, this invention is very unique in that Urea and calm" dlsulfida of f q l eachfndlcatcd ua carbonyl lfid and ammonium thiocyanate are in Table below were added to various reaction media such as formed from urea and carbon disulfide with high efficiency methanol, elhiinoli Pf' p three are the 'and ease. From the standpoint of industrial production, the f of thls invention) y y i glycerolr acetonc, subject invention further hasthe following advantages. dlmethylsulfoxide and dlOXane Controls). n

. o 9 It is known that carbonyl sulfide can be obtained by direct 35 'l'eacted 130 a Pressure glass Y The "Suns reaction of carbon monoxide with sulfur at 400-500 c. Howg nalye ns t e ga n ig ysfi res s gnja TABLE 2 Product's yield (based on urea) Starting materials Ammonium Carbon Carbonyl thio- Urea, disulfide, Temp Time, sulfide, cyanate. g. g. Reaction medium, g. min. percent percent 2. 0 3. 0 Methanol, 6 160 120 88 2.0 3.0 160 87 76 2.0 3.0 120 71 69 6.8 7.8 152 25 21 6. 8 7. 8 162 180 20 17 6.3 6.6 153 30 8 1. 0 1. 6 130 60 (I) 3.6 4.5 162 70 34 21 l Changed to reddish brown or black. 1 Trace. isyl lgya p ec n d W i ever, that process is apt to encounter difficult problems in in- EXAMPLE 2 Five g. of urea and 5 ml. of carbon disulfide were added to 7-12 ml. of methanol, and charged in a stainless steel reactor, to be reacted at l36-l39" C. for 3 hours under stirring. The analysis results of the reaction products are shown in Table 3.

Conversion to Ammonium Thiocyanate Incidentally, the crude ammonium thiocyanate contained 130,6 0C 50C trace of methyl carbamate (NH COOCH as impurities.

' 5 3o 51 73 EXAMPLE 3 73 4o 49 11 so 70 Urea and carbon disulfide were added to methanol, charged so 68 86 2 in a stainless steel reactor, and reacted at 120190 C. for 13 90 31 hours under stirring. As to the seven runs, the respective tem- :28 :3 I perature, reaction time, quantities of starting materials, and 160 a3 s7 7; analysis results of the products are shown in Table 4 below.

TABLE 4 Yield, percent Ammo- Starting materials, in grams Products in grams nlum Time, M01 ratio Carbonyl thiohr. CO(NH2)2ICS CO(NH2)1 CS: CHaOH COS CS2 CO2 Has Sulfide cyanat 3 l/1 5.00 6. 34 8.0 2.10 3.63 0.0 0.05 2.71 2.90 0.0 42.0 42. 2 1/1 5.00 6. 34 8.0 2. 62 2.85 0.012 0.05 2.95 2.13 0.0 52.4 46. 3 1/1 5.00 0.34 8.0 4.27 0.62 0.16 0. 095 4. 72 0. 34 0.22 85.4 74. 2 1/1 5.00 6.34 8.0 1. 86 1.62 0. 66 0. 44 2. 55 0.07 0.90 37.2 40. 1 l/1 5.00 6.34 8.0 0. 54 1.71 1.14 1.03 0.88 0.0 2.01 10.8 14. 3 1.5/1 7.5 6.34 8.0 4.61 0.15 0.018 0. 042 5.51 3.20 0. 24 4 92.2 4 87. 0 3 l/1.9 5.00 12.00 8.0 4. 71 5.78 0.016 0.15 4. 84 0.04 0.23 94.2 76. 2

1 NH4SCN. 4 Based on CS2. CO(NH2);. 5 Based on urea. 3 9 113 a We claim: EXAMPLE 4 1. A process for the simultaneous preparation of carbonyl 7 7 7 77 sulfide and ammonium thiocyanate, which comprises heating and reacting urea with carbon disulfide at liquid phase, in Twenty-five g. of urea and 31.7 g. of carbon disulfide (mol' 'alipllzmc monohydnc alcohol of one to four carbon atoms ratio 1;1 were d q q 497.0% f methanol, and reacted, serving as the reaction medium. in a stainless steel autoclave of 104 mlIhriapacityz a t each 3 5 The processc of clan? wherein the reaction temperature 130 C., 140 C., and 150 C. With the progress of the reaclranges from 100 to 9 {ion 1 to 2 m1 of the reaction mixture was successively l 3. The process of cla1m 1, wherein the reaction temperature a o 0 withdrawn from the system. The conversions thus calculated ranges from 120 to 9 (production ratio of ammonium thiocyanate) are shown in. 4. The process of cla1m 1, wherein the reaction time ranges Table 5. As can be understood from the table, the conversion 40 from 10 mmutes to 5 y to ammonium thiocyanate reaches the peak at a certain time, sgThePmcess of W h quanmyPf reacuon and thereafer shows a tendency of slow decreasa (Ammoni medium 1s at least sufficient to maintain the reaction mixture um thiocyanate was determined by titration of N/ AgNQ, at homogeneous phase the temperauire' Solution) 6. The process of cla1m 1, wherein the reaction medium 15 A. a. A ..1 methanol. 

2. The process of claim 1, wherein the reaction temperature ranges from 100* to 190* C.
 3. The process of claim 1, wherein the reaction temperature ranges from 120* to 160* C.
 4. The process of claim 1, wherein the reaction time ranges from 10 minutes to 5 hours.
 5. The process of claim 1, wherein the quantity of reaction medium is at least sufficient to maintain the reaction mixture at homogeneous phase at the reaction temperature.
 6. The process of claim 1, wherein the reaction medium is methanol. 